Electrosurgical working end with replaceable cartridges

ABSTRACT

An electrosurgical medical device and method for creating thermal welds in engaged tissue that carries the electrosurgical components in a disposable cartridge. The instrument also can carry a blade member in a disposable cartridge, thus making the instrument system inexpensive to use. In another embodiment, the electrical leads of the cartridge have a surface coating of a thermochromic material to provide the physician with a visual indicator of operational parameters when applying energy to tissue.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit from Provisional U.S. patent applicationSer. No. 60/362,689 filed May 23, 2002 having the same title as above,which application is incorporated herein by this reference. Thisapplication is a Continuation-In-Part of U.S. patent application Ser.No. 10/032,867 filed Oct. 22, 2001, now issued as U.S. Pat. No.6,929,644, titled Electrosurgical Jaw Structure for Controlled EnergyDelivery.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to medical devices and techniques and moreparticularly relates to an electrosurgical system that can apply energyto tissue from an engagement surface that modulates the Rf power levelsapplied to tissue across micron-scale portions of the engagementsurface, together with means for providing the electrosurgicalfunctionality in a disposable cartridge.

2. Description of the Related Art

In the prior art, various energy sources such as radiofrequency (Rf)sources, ultrasound sources and lasers have been developed to coagulate,seal or join together tissues volumes in open and laparoscopicsurgeries. The most important surgical application relates to sealingblood vessels which contain considerable fluid pressure therein. Ingeneral, no instrument working ends using any energy source have provenreliable in creating a “tissue weld” or “tissue fusion” that has veryhigh strength immediately post-treatment. For this reason, thecommercially available instruments, typically powered by Rf orultrasound, are mostly limited to use in sealing small blood vessels andtissues masses With microvasculature therein. The prior art Rf devicesalso fail to provide seals with substantial strength in anatomicstructures having walls with irregular or thick fibrous content, inbundles of disparate anatomic structures, in substantially thickanatomic structures, or in tissues with thick fascia layers (e.g., largediameter blood vessels).

In a basic bi-polar Rf jaw arrangement, each face of opposing first andsecond jaws comprises an electrode and Rf current flows across thecaptured tissue between the opposing polarity electrodes. Such prior artRf jaws that engage opposing sides of tissue typically cannot causeuniform thermal effects in the tissue—whether the captured tissue isthin or substantially thick. As Rf energy density in tissue increases,the tissue surface becomes desiccated and resistant to additional ohmicheating. Localized tissue desiccation and charring can occur almostinstantly as tissue impedance rises, which then can result in anon-uniform seal in the tissue. The typical prior art Rf jaws can causefurther undesirable effects by propagating Rf density laterally from theengaged tissue thus causing unwanted collateral thermal damage.

The commercially available Rf sealing instruments typically use one oftwo approaches to “control” Rf energy delivery in tissue. In a first“power adjustment” approach, the Rf system controller can rapidly adjustthe level of total power delivered to the jaws' engagement surfaces inresponse to feedback circuitry coupled to the active electrodes thatmeasures tissue impedance or electrode temperature. In a second“current-path directing” approach, the instrument jaws carry anelectrode arrangement in which opposing polarity electrodes are spacedapart by an insulator material—which may cause current to flow within anextended path through captured tissue rather that simply betweensurfaces of the first and second jaws. Electrosurgical graspinginstruments having jaws with electrically-isolated electrodearrangements in cooperating jaws faces were proposed by Yates et al. inU.S. Pat. Nos. 5,403,312; 5,735,848 and 5,833,690.

The illustrations of the wall of a blood vessel in FIGS. 1A–1D areuseful in understanding the limitations of prior art Rf working ends forsealing tissue. FIG. 1B provides a graphic illustration of the opposingvessel walls portions 2 a and 2 b with the tissue divided into a gridwith arbitrary micron dimensions—for example, the grid can represent 5microns on each side of the targeted tissue. In order to create the mosteffective “weld” in tissue, each micron-dimensioned volume of tissuemust be simultaneously elevated to the temperature needed to denatureproteins therein. As will be described in more detail below, in order tocreate a “weld” in tissue, collagen, elastin and other protein moleculeswithin an engaged tissue volume must be denatured by breaking the inter-and intra-molecular hydrogen bonds—followed by re-crosslinking onthermal relaxation to create a fused-together tissue mass. It can beeasily understood that ohmic heating in tissue-if not uniform—can atbest create localized spots of truly “welded” tissue. Such anon-uniformly denatured tissue volume still is “coagulated” and willprevent blood flow in small vasculature that contains little pressure.However, such non-uniformly denatured tissue will not create a seal withsignificant strength, for example in 2 mm. to 10 mm. arteries thatcontain high pressures.

Now turning to FIG. 1C, it is reasonable to ask whether the “poweradjustment” approach to energy delivery is likely to cause a uniformtemperature within every micron-scale tissue volume in the gridsimultaneously—and maintain that temperature for a selected timeinterval. FIG. 1C shows the opposing vessel walls 2 a and 2 b beingcompressed with cut-away phantom views of opposing polarity electrodeson either side of the tissue. One advantage of such an electrodearrangement is that 100% of each jaw engagement surface comprises an“active” conductor of electrical current—thus no tissue is engaged by aninsulator which theoretically would cause a dead spot (no ohmic heating)proximate to the insulator. FIG. 1C graphically depicts current “paths”p in the tissue at an arbitrary time interval that can be microseconds(μs) apart. Such current paths p would be random and constantly influx—along transient most conductive pathways through the tissue betweenthe opposing polarity electrodes. The thickness of the “paths” isintended to represent the constantly adjusting power levels. If oneassumes that the duration of energy density along any current path p iswithin the microsecond range before finding a new conductive path—andthe thermal relaxation time of tissue is the millisecond (ms) range,then what is the likelihood that such entirely random current paths willrevisit and maintain each discrete micron-scale tissue volume at thetargeted temperature before thermal relaxation? Since the hydration oftissue is constantly reduced during ohmic heating—any regions of moredesiccated tissue will necessarily lose its ohmic heating and will beunable to be “welded” to adjacent tissue volumes. The “power adjustment”approach probably is useful in preventing rapid overall tissuedesiccation. However, it is postulated that any approach that relies onentirely “random” current paths p in tissue—no matter the powerlevel—cannot cause contemporaneous denaturation of tissue constituentsin all engaged tissue volumes and thus cannot create an effectivehigh-strength “weld” in tissue.

Now referring to FIG. 1D, it is possible to evaluate the second“current-path directing” approach to energy delivery in a jaw structure.FIG. 1D depicts vessel walls 2 a and 2 b engaged between opposing jawssurfaces with cutaway phantom views of opposing polarity (+) and (−)electrodes on each side of the engaged tissue. An insulator indicated at10 is shown in cut-away view that electrically isolates the electrodesin the jaw. One significant disadvantage of using an insulator 10 in ajaw engagement surface is that no ohmic heating of tissue can bedelivered directly to the tissue volume engaged by the insulator 10 (seeFIG. 1D). The tissue that directly contacts the insulator 10 will onlybe ohmically heated when a current path p extends through the tissuebetween the spaced apart electrodes. FIG. 1D graphically depicts currentpaths p at any arbitrary time interval, for example in the μs range.Again, such current paths p will be random and in constant flux alongtransient conductive pathways.

This type of random, transient Rf energy density in paths p throughtissue, when any path may occur only for a microsecond interval, is notlikely to uniformly denature proteins in the entire engaged tissuevolume. It is believed that the “current-path directing” approach fortissue sealing can only accomplish tissue coagulation or seals withlimited strength.

Now turning to FIG. 2, it can be conceptually understood that the keyrequirements for thermally-induced tissue welding relate to: (i) meansfor “non-random spatial localization” of energy densities in the engagedtissue et, (ii) means for “controlled, timed intervals” of powerapplication of such spatially localized of energy densities, and (iii)means for “modulating the power level ” of any such localized,time-controlled applications of energy.

FIG. 2 illustrates a hypothetical tissue volume with a lower jaw'sengagement surface 15 backed away from the tissue. The tissue is engagedunder very high compression which is indicated by arrows in FIG. 2. Theengagement surface 15 is shown as divided into a hypothetical grid of“pixels” or micron-dimensioned surface areas 20. Thus, FIG. 2graphically illustrates that to create an effective tissue weld, thedelivery of energy should be controlled and non-randomly spatiallylocalized relative to each pixel 20 of the engagement surface 15.

Still referring to FIG. 2, it can be understood that there are twomodalities in which spatially localized, time-controlled energyapplications can create a uniform energy density in tissue for proteindenaturation. In a first modality, all cubic microns of the engagedtissue (FIG. 2) can be elevated to the required energy density andtemperature contemporaneously to create a weld. In a second modality, a“wave” of the required energy density can sweep across the engagedtissue et that can thereby leave welded tissue in its wake. The authorshave investigated, developed and integrated Rf systems for accomplishingboth such modalities—which are summarized in the next Section.

SUMMARY OF THE INVENTION

The systems and methods corresponding to invention relate to creatingthermal “welds” or “fusion” within native tissue volumes. Thealternative terms of tissue “welding” and tissue “fusion” are usedinterchangeably herein to describe thermal treatments of a targetedtissue volume that result in a substantially uniform fused-togethertissue mass that provides substantial tensile strength immediatelypost-treatment. Such tensile strength (no matter how measured) isparticularly important (i) for welding blood vessels in vesseltransection procedures, (ii) for welding organ margins in resectionprocedures, (iii) for welding other anatomic ducts wherein permanentclosure is required, and also (iv) for vessel anastomosis, vesselclosure or other procedures that join together anatomic structures orportions thereof.

The systems of the invention are useful for both endoscopic and opensurgeries. In one embodiment, a re-useable scissor-type instrument canbe provided with the electrosurgical component offered as a disposablecartridge. In one embodiment, the electrical lead of the cartridge has asurface coating of a thermochromic material to provide the physicianwith a visual indicator of operational parameters when applying energyto tissue. The instrument also can carry a blade member in a disposablecartridge, thus making the instrument system inexpensive to use.

The welding or fusion of tissue as disclosed herein is to bedistinguished from “coagulation”, “sealing”, “hemostasis” and othersimilar descriptive terms that generally relate to the collapse andocclusion of blood flow within small blood vessels or vascularizedtissue. For example, any surface application of thermal energy can causecoagulation or hemostasis—but does not fall into the category of“welding” as the term is used herein. Such surface coagulation does notcreate a weld that provides any substantial strength in the affectedtissue.

At the molecular level, the phenomena of truly “welding” tissue asdisclosed herein may not be fully understood. However, the authors haveidentified the parameters at which tissue welding can be accomplished.An effective “weld” as disclosed herein results from thethermally-induced denaturation of collagen, elastin and other proteinmolecules in a targeted tissue volume to create a transient liquid orgel-like proteinaceous amalgam. A selected energy density is provided inthe targeted tissue to cause hydrothermal breakdown of intra- andintermolecular hydrogen crosslinks in collagen and other proteins. Thedenatured amalgam is maintained at a selected level of hydration—withoutdesiccation—for a selected time interval which can be very brief. Thetargeted tissue volume is maintained under a selected very high level ofmechanical compression to insure that the unwound strands of thedenatured proteins are in close proximity to allow their intertwiningand entanglement. Upon thermal relaxation, the intermixed amalgamresults in “protein entanglement” as re-crosslinking or renaturationoccurs to thereby cause a uniform fused-together mass.

To better appreciate the scale at which thermally-induced proteindenaturation occurs—and at which the desired protein entanglement andre-crosslinking follows—consider that a collagen molecule in its nativestate has a diameter of about 15 Angstroms. The collagen moleculeconsists of a triple helix of peptide stands about 1000 Angstroms inlength (see FIG. 2). In other words—a single μm³ (cubic micrometer) oftissue that is targeted for welding will contain 10's of thousands ofsuch collagen molecules. In FIG. 2, each tissue volume in the gridrepresents an arbitrary size from about 1 μm to 5 μm (microns). Elastinand other molecules fro denaturation are believed to be similar indimension to collagen.

To weld tissue, or more specifically to thermally-induce proteindenaturation, and subsequent entanglement and re-crosslinking in atargeted tissue volume, it has been learned that the followinginterlinked parameters must be controlled:

(i) Temperature of thermal denaturation. The targeted tissue volume mustbe elevated to the temperature of thermal denaturation, T_(d), whichranges from about 50° C. to 90° C., and more specifically is from about60° C. to 80° C. The optimal T_(d) within the larger temperature rangeis further dependent on the duration of thermal effects and level ofpressure applied to the engaged tissue.

(ii) Duration of treatment. The thermal treatment must extend over aselected time duration, which depending on the engaged tissue volume,can range from less than 0.1 second to about 5 seconds. As will bedescribed below, the system of the in invention utilizes a thermaltreatment duration ranging from about 500 ms second to about 3000 ms.Since the objectives of protein entanglement occur at T_(d) which can beachieved in ms (or even microseconds)—this disclosure will generallydescribe the treatment duration in ms.

(iii) Ramp-up in temperature; uniformity of temperature profile. Thereis no limit to the speed at which temperature can be ramped up withinthe targeted tissue. However, it is of utmost importance to maintain avery uniform temperature across the targeted tissue volume so that “all”proteins are denatured within the same microsecond interval. Onlythermal relaxation from a uniform temperature T_(d) can result incomplete protein entanglement and re-crosslinking across an entiretissue volume. Without such uniformity of temperature ramp-up andrelaxation, the treated tissue will not become a fused-together tissuemass—and thus will not have the desired strength.

Stated another way, it is necessary to deposit enough energy into thetargeted volume to elevate it to the desired temperature T_(d) before itdiffuses into adjacent tissue volumes. The process of heat diffusiondescribes a process of conduction and convection and defines a targetedvolume's thermal relaxation time (often defined as the time over whichthe temperature is reduced by one-half). Such thermal relaxation timescales with the square of the diameter of the treated volume in aspherical volume, decreasing as the diameter decreases. In general,tissue is considered to have a thermal relaxation time in the range of 1ms. In a non-compressed tissue volume, or lightly compressed tissuevolume, the thermal relaxation of tissue in an Rf application typicallywill prevent a uniform weld since the random current paths result invery uneven ohmic heating (see FIGS. 1C–1D).

(iv) Instrument engagement surfaces. The instrument's engagementsurface(s) must have characteristics that insure that every squaremicron of the instrument surface is in contact with tissue during Rfenergy application. Any air gap between an engagement surface and tissuecan cause an arc of electrical energy across the insulative gap thusresulting in charring of tissue. Such charring (desiccation) willentirely prevent welding of the localized tissue volume and result infurther collateral effects that will weaken any attempted weld. For thisreason, the engagement surfaces corresponding to the invention are (i)substantially smooth at a macroscale, and (ii) at least partly of anelastomeric matrix that can conform to the tissue surface dynamicallyduring treatment. The jaw structure of the invention typically hasgripping elements that are lateral from the energy-delivering engagementsurfaces. Gripping serrations otherwise can cause unwanted “gaps” andmicroscale trapped air pockets between the tissue and the engagementsurfaces.

(v) Pressure. It has been found that very high external mechanicalpressures on a targeted tissue volume are critical in welding tissue—forexample, between the engagement surfaces of a jaw structure. In oneaspect, as described above, the high compressive forces can cause thedenatured proteins to be crushed together thereby facilitating theintermixing or intercalation of denatured protein stands whichultimately will result in a high degree of cross-linking upon thermalrelaxation.

In another aspect, the proposed high compressive forces (it is believed)can increase the thermal relaxation time of the engaged tissuepractically by an infinite amount. With the engaged tissue highlycompressed to the dimension of a membrane between opposing engagementsurfaces, for example to a thickness of about 0.001″, there iseffectively little “captured” tissue within which thermal diffusion cantake place. Further, the very thin tissue cross-section at the marginsof the engaged tissue prevents heat conduction to tissue volumes outsidethe jaw structure.

In yet another aspect, the high compressive forces at first cause thelateral migration of fluids from the engaged tissue which assists in thesubsequent welding process. It has been found that highly hydratedtissues are not necessary in tissue welding. What is important ismaintaining the targeted tissue at a selected level without desiccationas is typical in the prior art. Further, the very high compressiveforces cause an even distribution of hydration across the engaged tissuevolume prior to energy delivery.

In yet another aspect, the high compressive forces insure that theengagement planes of the jaws are in complete contact with the surfacesof the targeted tissues, thus preventing any possibility of an arc ofelectrical energy a cross a “gap” would cause tissue charring, asdescribed previously.

One exemplary embodiment disclosed herein is particularly adapted for,in effect, independent spatial localization and modulation of Rf energyapplication across micron-scale “pixels” of an engagement surface. Thejaw structure of the instrument defines opposing engagement planes thatapply high mechanical compression to the engaged tissue. At least oneengagement plane has a surface layer that comprises first and secondportions of a conductive-resistive matrix—preferably including anelastomer such as silicone (first portion) and conductive particles(second portion) distributed therein. An electrical source is coupled tothe working end such that the combination of the conductive-resistivematrix and the engaged tissue are intermediate opposing conductors thatdefine first and second polarities of the electrical source coupledthereto. The conductive-resistive matrix is designed to exhibit uniqueresistance vs. temperature characteristics, wherein the matrix maintainsa low base resistance over a selected temperature range with adramatically increasing resistance above a selected narrow temperaturerange.

In operation, it can be understood that current flow through theconductive-resistive matrix and engagement plane will apply active Rfenergy (ohmic heating) to the engaged tissue until the point in timethat any portion of the matrix is heated to a range that substantiallyreduces its conductance. This effect will occur across the surface ofthe matrix thus allowing each matrix portion to deliver an independentlevel of power therethrough. This instant, localized reduction of Rfenergy application can be relied on to prevent any substantialdehydration of tissue proximate to the engagement plane. The systemeliminates the possibility of desiccation thus meeting another of theseveral parameters described above.

The conductive-resistive matrix and jaw body corresponding to theinvention further can provides a suitable cross-section and mass forproviding substantial heat capacity. Thus, when the matrix is elevatedin temperature to the selected thermal treatment range, the retainedheat of the matrix volume can effectively apply thermal energy to theengaged tissue volume by means of conduction and convection. Inoperation, the working end can automatically modulate the application ofenergy to tissue between active Rf heating and passive conductiveheating of the targeted tissue to maintain a targeted temperature level.

Of particular interest, another system embodiment disclosed herein isadapted for causing a “wave” of ohmic heating to sweep across tissue todenature tissue constituents in its wake. This embodiment again utilizesat least one engagement plane in a jaw structure that carries aconductive-resistive matrix as described previously. At least one of theopposing polarity conductors has a portion thereof exposed in theengagement plane. The conductive-resistive matrix again is intermediatethe opposing polarity conductors. When power delivery is initiated, thematrix defines an “interface” therein where microcurrents are mostintense about the interface of the two polarities—since the matrix isnot a simple conductor. The engaged tissue, in effect, becomes anextension of the interface of microcurrents created by the matrix—whichthus localizes ohmic heating across the tissue proximate the interface.The interface of polarities and microcurrents within the matrix will bein flux due to lesser conductance about the interface as the matrix iselevated in temperature. Thus, a “wave-like” zone of microcurrentsbetween the polarities will propagate across the matrix—and across theengaged tissue. By this means of engaging tissue with aconductive-resistive matrix, a wave of energy density can be caused tosweep across tissue to uniformly denature proteins which will thenre-crosslink to create a uniquely strong weld.

In general, the system of conductive-resistive matrices for Rf energydelivery advantageously provides means for spatial-localization andmodulation, of energy application from selected, discrete locationsacross a single energy-emitting surface coupled to a single energysource

The system of conductive-resistive matrices for Rf energy deliveryprovides means for causing a dynamic wave of ohmic heating in tissue topropagate across engaged tissue.

The system of conductive-resistive matrices for Rf energy deliveryallows for opposing electrical potentials to be exposed in a singleengagement surface with a conductive matrix therebetween to allow 100%of the engagement surface to emit energy to tissue.

The system of conductive-resistive matrices for Rf energy application totissue allows for bi-polar electrical potential to be exposed in asingle engagement surface without an intermediate insulator portion.

The system of conductive-resistive matrices for energy delivery allowsfor the automatic modulation of active ohmic heating and passive heatingby conduction and convection to treat tissue.

The system of conductive-resistive matrices for energy application totissue advantageously allows for the creation of “welds” in tissuewithin about 500 ms to 2 seconds.

The system of conductive-resistive matrices for energy application totissue provides “welds” in blood vessels that have very high strength.

Additional objects and advantages of the invention will be apparent fromthe following description, the accompanying drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a view of a blood vessel targeted for welding.

FIG. 1B is a greatly enlarged sectional view of opposing wall portionsof the blood vessel of FIG. 1A taken along line 1B—1B of FIG. 1A.

FIG. 1C is a graphic representation of opposing walls of a blood vesselengaged by prior art electrosurgical jaws showing random paths ofcurrent (causing ohmic heating) across the engaged tissue betweenopposing polarity electrodes.

FIG. 1D is a graphic representation of a blood vessel engaged by priorart electrosurgical jaws with an insulator between opposing polarityelectrodes on each side of the tissue showing random paths of current(ohmic heating).

FIG. 2 graphically represents a blood vessel engaged by hypotheticalelectrosurgical jaws under very high compression with an energy-deliverysurface proximate to the tissue.

FIG. 3A is a perspective view of a jaw structure of tissue-transectingand welding instrument that carries a Type “A” conductive-resistivematrix system corresponding to the invention.

FIG. 3B is a sectional view of the jaw structure of FIG. 3A taken alongline 3B—3B of FIG. 3A showing the location of conductive-resistivematrices.

FIG. 4 is a perspective view of another exemplary surgical instrumentthat carries a Type “A” conductive-resistive matrix system for weldingtissue.

FIG. 5 is a sectional view of the jaw structure of FIG. 4 taken alongline 5—5 of FIG. 4 showing details of the conductive-resistive matrix.

FIG. 6 is a graph showing (i) temperature-resistance profiles ofalternative conductive-resistive matrices that can be carried in the jawof FIG. 5, (ii) the impedance of tissue, and (iii) the combinedresistance of the matrix and tissue as measured by a system controller.

FIG. 7A is an enlarged view of a portion of the conductive-resistivematrix and jaw body of FIG. 5 showing a first portion of an elastomerand a second portion of conductive particles at a resting temperature.

FIG. 7B is another view the conductive-resistive matrix and jaw body ofFIG. 7A after a portion is elevated to a higher temperature to modulatemicrocurrent flow therethrough thus depicting a method of the inventionin spatially localizing and modulating Rf energy application from aconductive-resistive matrix that engages tissue.

FIG. 8A is a further enlarged view of the conductive-resistive matrix ofFIG. 7A showing the first portion (elastomer) and the second portion(conductive elements) and paths of microcurrents therethrough.

FIG. 8B is a further enlarged view of matrix of FIG. 7B showing theeffect of increased temperature and the manner in which resistance tomicrocurrent flow is caused in the method of spatially localizing andmodulating Rf energy application.

FIG. 9 is an enlarged view of an alternative conductive-resistive matrixsimilar to that of FIG. 7A that is additionally doped with thermallyconductive, electrically non-conductive particles.

FIG. 10 is an alternative jaw structure similar to that of FIGS. 5 and7A except carrying conductive-resistive matrices in the engagementsurfaces of both opposing jaws.

FIG. 11 is a greatly enlarged sectional view of the jaws of FIG. 10taken along line 11—11 of FIG. 10.

FIG. 12 is a sectional view of another exemplary jaw structure thatcarries a Type “B” conductive-resistive matrix system for welding tissuethat utilizes opposing polarity electrodes with an intermediateconductive-resistive matrix in an engagement surface.

FIG. 13A is a sectional view of alternative Type “B” jaw with aplurality of opposing polarity electrodes with intermediateconductive-resistive matrices in the engagement surface.

FIG. 13B is a sectional view of a Type “B” jaw similar to that of FIG.13A with a plurality of opposing polarity electrodes with intermediateconductive-resistive matrices in the engagement surface in a differentangular orientation.

FIG. 13C is a sectional view of another Type “B” jaw similar to that ofFIGS. 13A–13B with a plurality of opposing polarity electrodes withintermediate matrices in another angular orientation.

FIGS. 14A–14C graphically illustrate a method of the invention incausing a wave of Rf energy density to propagate across and engagedtissue membrane to denature tissue constituents:

FIG. 14A being the engagement surface of FIG. 12 engaging tissuemembrane at the time that energy delivery is initiated causing localizedmicrocurrents and ohmic tissue heating;

FIG. 14B being the engagement surface of FIG. 12 after an arbitrarymillisecond or microsecond time interval depicting the propagation of awavefronts of energy outward from the initial localized microcurrents asthe localized temperature and resistance of the matrix is increased; and

FIG. 14C being the engagement surface of FIG. 12 after another verybrief interval depicting the propagation of the wavefronts of energydensity outwardly in the tissue due to increase temperature andresistance of matrix portions.

FIG. 15 is an enlarged sectional view of the exemplary jaw structure ofFIG. 13A with a plurality of opposing polarity conductors on either sideof conductive-resistive matrix portions.

FIG. 16 is a sectional view of a jaw structure similar to that of FIG.15 with a plurality of opposing polarity conductors that float within anelastomeric conductive-resistive matrix portions.

FIG. 17 is a sectional view of a jaw structure similar to that of FIG.16 with a single central conductor that floats on a convex elastomericconductive-resistive matrix with opposing polarity conductors inoutboard locations.

FIGS. 18A–18C provide simplified graphic views of the method of causinga wave of Rf energy density in the embodiment of FIG. 17, similar to themethod shown in FIGS. 14A–14C:

FIG. 18A corresponding to the view of FIG. 14A showing initiation ofenergy delivery;

FIG. 18B corresponding to the view of FIG. 14B showing the propagationof the wavefronts of energy density outwardly; and

FIG. 18C corresponding to the view of FIG. 14C showing the furtheroutward propagation of the wavefronts of energy density to thereby weldtissue.

FIG. 19 is a sectional view of another exemplary jaw structure thatcarries two conductive-resistive matrix portions, each having adifferent durometer and a different temperature coefficient profile.

FIG. 20 is a sectional view of a jaw assembly having the engagementplane of FIG. 17 carried in a transecting-type jaws similar to that ofFIGS. 3A–3B.

FIG. 21 is a perspective view of a Type “C” scissor-type instrument witha jaw structure similar to Types “A”–“B” embodiments with (i) adisposable cartridge that carries a conductive-resistive matrix systemaccording to the invention and (ii) a disposable cartridge that carriesa transecting knife blade (shown in an extended position).

FIG. 22 is a sectional view of the working end of the opposing jaws andconductive-resistive matrix system of FIG. 21 taken along line 22—22 ofFIG. 21.

FIG. 23 is an exploded view of the components of the Type “C”scissor-type instrument of FIG. 21 with the disposable electrosurgicalcartridge and the disposable blade cartridge de-mated form the scissorarms.

FIG. 24 is an alternative embodiment of a Type “C” scissor-type jawstructure similar to that of FIG. 21 except carrying a rotatable bladeelement.

FIG. 25 is an electrical lead or cable of an electrosurgical instrumentthat carries a thermochromic layer for providing a visual indicator tothe physician.

FIG. 26 is an alternative flex circuit electrical lead of anelectrosurgical instrument that carries a thermochromic layer forproviding a visual indicator to the physician.

DETAILED DESCRIPTION OF THE INVENTION

1. Exemplary jaw structures for welding tissue. FIGS. 3A and 3Billustrate a working end of a surgical grasping instrument correspondingto the invention that is adapted for transecting captured tissue and forcontemporaneously welding the captured tissue margins with controlledapplication of Rf energy. The jaw assembly 100A is carried at the distalend 104 of an introducer sleeve member 106 that can have a diameterranging from about 2 mm. to 20 mm. for cooperating with cannulae inendoscopic surgeries or for use in open surgical procedures. Theintroducer portion 106 extends from a proximal handle (not shown). Thehandle can be any type of pistol-grip or other type of handle known inthe art that carries actuator levers, triggers or sliders for actuatingthe jaws and need not be described in further detail. The introducersleeve portion 106 has a bore 108 extending therethrough for carryingactuator mechanisms for actuating the jaws and for carrying electricalleads 109 a–109 b for delivery of electrical energy to electrosurgicalcomponents of the working end.

As can be seen in FIGS. 3A and 3B, the jaw assembly 100A has first(lower) jaw element 112A and second (upper) jaw element 112B that areadapted to close or approximate about axis 115. The jaw elements canboth be moveable or a single jaw can rotate to provide the jaw-open andjaw-closed positions. In the exemplary embodiment of FIGS. 3A and 3B,both jaws are moveable relative to the introducer portion 106.

Of particular interest, the opening-closing mechanism of the jawassembly 100A is capable of applying very high compressive forces ontissue on the basis of cam mechanisms with a reciprocating member 140.The engagement surfaces further provide a positive engagement of cammingsurfaces (i) for moving the jaw assembly to the (second) closed positionto apply very high compressive forces, and (ii) for moving the jawstoward the (first) open position to apply substantially high openingforces for “dissecting” tissue. This important feature allows thesurgeon to insert the tip of the closed jaws into a dissectable tissueplane—and thereafter open the jaws to apply such dissecting forcesagainst tissues. Prior art instruments are spring-loaded toward the openposition which is not useful for dissecting tissue.

In the embodiment of FIGS. 3A and 3B, a reciprocating member 140 isactuatable from the handle of the instrument by any suitable mechanism,such as a lever arm, that is coupled to a proximal end 141 of member140. The proximal end 141 and medial portion of member 140 aredimensioned to reciprocate within bore 108 of introducer sleeve 106. Thedistal portion 142 of reciprocating member 140 carries first (lower) andsecond (upper) laterally-extending flange elements 144A and 144B thatare coupled by an intermediate transverse element 145. The transverseelement further is adapted to transect tissue captured between the jawswith a leading edge 146 (FIG. 3A) that can be a blade or a cuttingelectrode. The transverse element 145 is adapted to slide within achannels 148 a and 148 b in the paired first and second jaws to therebyopen and close the jaws. The camming action of the reciprocating member140 and jaw surfaces is described in complete detail in co-pendingProvisional U.S. patent application Ser. No. 60/347,382 filed Jan. 11,2002 titled Jaw Structure for Electrosurgical Instrument and Method ofUse, which is incorporated herein by reference.

In FIGS. 3A and 3B, the first and second jaws 112A and 112B close aboutan engagement plane 150 and define tissue-engaging surface layers 155Aand 155B that contact and deliver energy to engaged tissues fromelectrical energy means as will be described below. The jaws can haveany suitable length with teeth or serrations 156 for gripping tissue.One preferred embodiment of FIGS. 3A and 3B provides such serrations 156at an inner portion of the jaws along channels 148 a and 148 b thusallowing for substantially smooth engagement surface layers 155A and155B laterally outward of the tissue-gripping elements. The axial lengthof jaws 112A and 112B indicated at L can be any suitable lengthdepending on the anatomic structure targeted for transection and sealingand typically will range from about 10 mm. to 50 mm. The jaw assemblycan apply very high compression over much longer lengths, for example upto about 200 mm., for resecting and sealing organs such as a lung orliver. The scope of the invention also covers jaw assemblies for aninstrument used in micro-surgeries wherein the jaw length can be about5.0 mm or less.

In the exemplary embodiment of FIGS. 3A and 3B, the engagement surface155A of the lower jaw 112A is adapted to deliver energy to tissue, atleast in part, through a conductive-resistive matrix CM corresponding tothe invention. The tissue-contacting surface 155B of upper jaw 112Bpreferably carries a similar conductive-resistive matrix, or the surfacecan be a conductive electrode or and insulative layer as will bedescribed below. Alternatively, the engagement surfaces of the jaws cancarry any of the energy delivery components disclosed in co-pending U.S.patent application Ser. No. 10/032,867 filed Oct. 22, 2001 titledElectrosurgical Jaw Structure for Controlled Energy Delivery and U.S.patent application Ser. No. 10/308,362 filed Dec. 3, 2002 titledElectrosurgical Jaw Structure for Controlled Energy Delivery, both ofwhich are incorporated herein by reference.

Referring now to FIG. 4, an alternative jaw structure 100B is shown withlower and upper jaws having similar reference numerals 112A–112B. Thesimple scissor-action of the jaws in FIG. 4 has been found to be usefulfor welding tissues in procedures that do not require tissuetransection. The scissor-action of the jaws can apply high compressiveforces against tissue captured between the jaws to perform the methodcorresponding to the invention. As can be seen by comparing FIGS. 3B and4, the jaws of either embodiment 100A or 100B can carry the same energydelivery components, which is described next.

It has been found that very high compression of tissue combined withcontrolled Rf energy delivery is optimal for welding the engaged tissuevolume contemporaneous with transection of the tissue. Preferably, theengagement gap g between the engagement planes ranges from about 0.0005″to about 0.050″ for reduce the engaged tissue to the thickness of amembrane. More preferably, the gap g between the engagement planesranges from about 0.001″ to about 0.005″.

2. Type “A” conductive-resistive matrix system for controlled energydelivery in tissue welding. FIG. 5 illustrates an enlarged schematicsectional view of a jaw structure that carries engagement surface layers155A and 155B in jaws 112A and 112B. It should be appreciated that theengagement surface layers 155A and 155B are shown in a scissors-type jaw(cf. FIG. 4) for convenience, and the conductive-resistive matrix systemwould be identical in each side of a transecting jaw structure as shownin FIGS. 3A–3B.

In FIG. 5, it can be seen that the lower jaw 112A carries a componentdescribed herein as a conductive-resistive matrix CM that is at leastpartly exposed to an engagement plane 150 that is defined as theinterface between tissue and a jaw engagement surface layer, 155A or155B. More in particular, the conductive-resistive matrix CM comprises afirst portion 160 a and a second portion 160 b. The first portion ispreferably an electrically nonconductive material that has a selectedcoefficient of expansion that is typically greater than the coefficientof expansion of the material of the second portion. In one preferredembodiment, the first portion 160 a of the matrix is an elastomer, forexample a medical grade silicone. The first portion 160 a of the matrixalso is preferably not a good thermal conductor. Other thermoplasticelastomers fall within the scope of the invention, as do ceramics havinga thermal coefficient of expansion with the parameters further describedbelow.

Referring to FIG. 5, the second portion 160 b of the matrix CM is amaterial that is electrically conductive and that is distributed withinthe first portion 160 a. In FIG. 5, the second portion 160 b isrepresented (not-to-scale) as spherical elements 162 that are intermixedwithin the elastomer first portion 160 a of matrix CM. The elements 162can have any regular or irregular shape, and also can be elongatedelements or can comprise conductive filaments. The dimensions ofelements 162 can range from nanoparticles having a scale of about 1 nm.to 2 nm. across a principal axis thereof to much larger cross-sectionsof about 100 microns in a typical jaw structure. In a very large jaw,the elements 162 in matrix CM can have a greater dimension that 100microns in a generally spherical form. Also, the matrix CM can carry asecond portion 160 b in the form of an intertwined filament (orfilaments) akin to the form of steel wool embedded within an elastomericfirst portion 160 a and fall within the scope the invention. Thus, thesecond portion 160 b can be of any form that distributes an electricallyconductive mass within the overall volume of the matrix CM.

In the lower jaw 112A of FIG. 5, the matrix CM is carried in a supportstructure or body portion 158 that can be of any suitable metal or othermaterial having sufficient strength to apply high compressive forces tothe engaged tissue. Typically, the support structure 158 carries aninsulative coating 159 to prevent electrical current flow to tissuesabout the exterior of the jaw assembly and between support structure 158and the matrix CM and a conductive element 165 therein.

Of particular interest, the combination of first and second portions 160a and 160 b provide a matrix CM that is variably resistive (inohms-centimeters) in response to temperature changes therein. The matrixcomposition with the temperature-dependent resistance is alternativelydescribed herein as a temperature coefficient material. In oneembodiment, by selecting the volume proportion of first portion 160 a ofthe non-conductive elastomer relative to the volume proportion of secondportion 160 b of the conductive nanoparticles or elements 162, thematrix CM can be engineered to exhibit very large changes in resistancewith a small change in matrix temperature. In other words, the change ofresistance with a change in temperature results in a “positive”temperature coefficient of resistance.

In a first preferred embodiment, the matrix CM is engineered to exhibitunique resistance vs. temperature characteristics that is represented bya positively sloped temperature-resistance curve (see FIG. 6). More inparticular, the first exemplary matrix CM indicated in FIG. 6 maintainsa low base resistance over a selected base temperature range with adramatically increasing resistance above a selected narrow temperaturerange of the material (sometimes referred to herein as a switchingrange, see FIG. 6). For example, the base resistance can be low, or theelectrical conductivity high, between about 37° C. and 65° C., with theresistance increasing greatly between about 65° C. and 75° C. tosubstantially limit conduction therethrough (at typically utilized powerlevels in electrosurgery). In a second exemplary matrix embodimentdescribed in FIG. 6, the matrix CM is characterized by a morecontinuously positively sloped temperature-resistance over the range of50° C. to about 80° C. Thus, the scope of the invention includes anyspecially engineered matrix CM with such a positive slope that issuitable for welding tissue as described below.

In one preferred embodiment, the matrix CM has a first portion 160 afabricated from a medical grade silicone that is doped with a selectedvolume of conductive particles, for example carbon particles insub-micron dimensions as described above. By weight, the ration ofsilicone-to-carbon can range from about 10/90 to about 70/30(silicone/carbon) to provide the selected range at which the inventivecomposition functions to substantially limit electrical conductancetherethrough. More preferably, the carbon percentage in the matrix CM isfrom about 40% to 80% with the balance being silicone. In fabricating amatrix CM in this manner, it is preferable to use a carbon type that hassingle molecular bonds. It is less preferable to use a carbon type withdouble bonds that has the potential of breaking down when used in asmall cross-section matrix, thus creating the potential of a permanentconductive path within deteriorated particles of the matrix CM that fusetogether. One preferred composition has been developed to provide athermal treatment range of about 75° C. to 80° C. with the matrix havingabout 50–60 percent carbon the balance being silicone. The matrix CMcorresponding to the invention thus becomes reversibly resistant toelectric current flow at the selected higher temperature range, andreturns to be substantially conductive within the base temperaturerange. In one preferred embodiment, the hardness of the silicone-basedmatrix CM is within the range of about Shore A range of less than about95. More preferably, an exemplary silicone-based matrix CM has Shore Arange of from about 20–80. The preferred hardness of the silicone-basedmatrix CM is about 150 or lower in the Shore D scale. As will bedescribed below, some embodiments have jaws that carry cooperatingmatrix portions having at least two different hardness ratings.

In another embodiment, the particles or elements 162 can be a polymerbead with a thin conductive coating. A metallic coating can be depositedby electroless plating processes or other vapor deposition process knownin the art, and the coating can comprise any suitable thin-filmdeposition, such as gold, platinum, silver, palladium, tin, titanium,tantalum, copper or combinations or alloys of such metals, or variedlayers of such materials. One preferred manner of depositing a metalliccoating on such polymer elements comprises an electroless platingprocess provided by Micro Plating, Inc., 8110 Hawthorne Dr., Erie, Pa.16509-4654. The thickness of the metallic coating can range from about0.00001″ to 0.005″. (A suitable conductive-resistive matrix CM cancomprise a ceramic first portion 160 a in combination withcompressible-particle second portion 160 b of a such a metallizedpolymer bead to create the effects illustrated in FIGS. 8A–8B below).

One aspect of the invention relates to the use of a matrix CM asillustrated schematically in FIG. 5 in a jaw's engagement surface layer155A with a selected treatment range between a first temperature (TE₁)and a second temperature (TE₂) that approximates the targeted tissuetemperature for tissue welding (see FIG. 6). The selected switchingrange of the matrix as defined above, for example, can be anysubstantially narrow 1°–10° C. range that is about the maximum of thetreatment range that is optimal for tissue welding. For anotherthermotherpy, the switching range can fall within any larger tissuetreatment range of about 50°–200° C.

No matter the character of the slope of the temperature-resistance curveof the matrix CM (see FIG. 6), a preferred embodiment has a matrix CMthat is engineered to have a selected resistance to current flow acrossits selected dimensions in the jaw assembly, when at 37° C. that rangesfrom about 0.0001 ohms to 1000 ohms. More preferably, the matrix CM hasa designed resistance across its selected dimensions at 37° C. thatranges from about 1.0 ohm to 1000 ohms. Still more preferably, thematrix CM has with a designed resistance across its selected dimensionsat 37° C. that ranges from about 25 ohms to 150 ohms. In any event, theselected resistance across the matrix CM in an exemplary jaw at 37° C.matches or slightly exceeds the resistance of the tissue or bodystructure that is engaged. The matrix CM further is engineered to have aselected conductance that substantially limits current flow thereroughcorresponding to a selected temperature that constitutes the high end(maximum) of the targeted thermal treatment range. As generallydescribed above, such a maximum temperature for tissue welding can be aselected temperature between about 50° C. and 90° C. More preferably,the selected temperature at which the matrix's selected conductancesubstantially limits current flow occurs at between about 60° C. and 80°C.

In the exemplary jaw 112A of FIG. 5, the entire surface area ofengagement surface layer 155A comprises the conductive-resistive matrixCM, wherein the engagement surface is defined as the tissue-contactingportion that can apply electrical potential to tissue. Preferably, anyinstrument's engagement surface has a matrix CM that comprises at least5% of its surface area. More preferably, the matrix CM comprises atleast 10% of the surface area of engagement surface. Still morepreferably, the matrix CM comprises at least 20% of the surface area ofthe jaw's engagement surface. The matrix CM can have any suitablecross-sectional dimensions, indicated generally at md₁ and md₂ in FIG.5, and preferably such a cross-section comprises a significantfractional volume of the jaw relative to support structure 158. As willbe described below, in some embodiments, it is desirable to provide athermal mass for optimizing passive conduction of heat to engagedtissue.

As can be seen in FIG. 5, the interior of jaw 112A carries a conductiveelement (or electrode) indicated at 165 that interfaces with an interiorsurface 166 of the matrix CM. The conductive element 165 is coupled byan electrical lead 109 a to a voltage (Rf) source 180 and optionalcontroller 182 (FIG. 4). Thus, the Rf source 180 can apply electricalpotential (of a first polarity) to the matrix CM through conductor165—and thereafter to the engagement plane 150 through matrix CM. Theopposing second jaw 112B in FIG. 5 has a conductive material (electrode)indicated at 185 coupled to source 180 by lead 109 b that is exposedwithin the upper engagement surface 155B.

In a first mode of operation, referring to FIG. 5, electrical potentialof a first polarity applied to conductor 165 will result in current flowthrough the matrix CM and the engaged tissue et to the opposing polarityconductor 185. As described previously, the resistance of the matrix CMat 37° C. is engineered to approximate, or slightly exceed, that of theengaged tissue et. It can now be described how the engagement surface155A can modulate the delivery of energy to tissue et similar to thehypothetical engagement surface of FIG. 2. Consider that the smallsections of engagement surfaces represent the micron-sized, surfaceareas (or pixels) of the illustration of FIG. 2 (note that the jaws arenot in a fully closed position in FIG. 5). The preferred membrane-thickengagement gap g is graphically represented in FIG. 5.

FIGS. 7A and 8A illustrate enlarged schematic sectional views of jaws112A and 112B and the matrix CM. It can be understood that theelectrical potential at conductor 165 will cause current flow within andabout the elements 162 of second portion 160 b along any conductive pathtoward the opposing polarity conductor 185. FIG. 8A more particularlyshows a graphic representation of paths of microcurrents mc_(m) withinthe matrix wherein the conductive elements 162 are in substantialcontact. FIG. 7A also graphically illustrates paths of microcurrentsmc_(t) in the engaged tissue across gap g. The current paths in thetissue (across conductive sodium, potassium, chlorine ions etc.) thusresults in ohmic heating of the tissue engaged between jaws 112A and112B. In fact, the flux of microcurrents mc_(m) within the matrix andthe microcurrents mc_(t) within the engaged tissue will seek the mostconductive paths—which will be assisted by the positioning of elements162 in the surface of the engagement layer 155A, which can act likesurface asperities or sharp edges to induce current flow therefrom.

Consider that ohmic heating (or active heating) of the shaded portion188 of engaged tissue et in FIGS. 7B and 8B elevates its temperature toa selected temperature at the maximum of the targeted range. Heat willbe conducted back to the matrix portion CM proximate to the heatedtissue. At the selected temperature, the matrix CM will substantiallyreduce current flow therethrough and thus will contribute less and lessto ohmic tissue heating, which is represented in FIGS. 7B and 8B. InFIGS. 7B and 8B, the thermal coefficient of expansion of the elastomerof first matrix portion 160 a will cause slight redistribution of thesecond conductive portion 160 b within the matrix—naturally resulting inlessened contacts between the conductive elements 162. It can beunderstood by arrows A in FIG. 8B that the elastomer will expand indirections of least resistance which is between the elements 162 sincethe elements are selected to be substantially resistant to compression.

Of particular interest, the small surface portion of matrix CM indicatedat 190 in FIG. 8A will function, in effect, independently to modulatepower delivery to the surface of the tissue T engaged thereby. Thiseffect will occur across the entire engagement surface layer 155A, toprovide practically infinite “spatially localized” modulation of activeenergy density in the engaged tissue. In effect, the engagement surfacecan be defined as having “pixels” about its surface that areindependently controlled with respect to energy application to localizedtissue in contact with each pixel. Due to the high mechanicalcompression applied by the jaws, the engaged membrane all can beelevated to the selected temperature contemporaneously as each pixelheats adjacent tissue to the top of treatment range. As also depicted inFIG. 8B, the thermal expansion of the elastomeric matrix surface alsowill push into the membrane, further insuring tissue contact along theengagement plane 150 to eliminate any possibility of an energy arcacross a gap.

Of particular interest, as any portion of the conductive-resistivematrix CM falls below the upper end of targeted treatment range, thatmatrix portion will increase its conductance and add ohmic heating tothe proximate tissue via current paths through the matrix from conductor165. By this means of energy delivery, the mass of matrix and the jawbody will be modulated in temperature, similar to the engaged tissue, ator about the targeted treatment range.

FIG. 9 shows another embodiment of a conductive-resistive matrix CM thatis further doped with elements 192 of a material that is highlythermally conductive with a selected mass that is adapted to providesubstantial heat capacity. By utilizing such elements 192 that may notbe electrically conductive, the matrix can provide greater thermal massand thereby increase passive conductive or convective heating of tissuewhen the matrix CM substantially reduces current flow to the engagedtissue. In another embodiment (not shown) the material of elements 162can be both substantially electrically conductive and highly thermallyconductive with a high heat capacity.

The manner of utilizing the system of FIGS. 7A–7B to perform the methodof the invention can be understood as mechanically compressing theengaged tissue et to membrane thickness between the first and secondengagement surfaces 155A and 155B of opposing jaws and thereafterapplying electrical potential of a frequency and power level known inelectrosurgery to conductor 165, which potential is conducted throughmatrix CM to maintain a selected temperature across engaged tissue etfor a selected time interval. At normal tissue temperature, the low baseresistance of the matrix CM allows unimpeded Rf current flow fromvoltage source 180 thereby making 100 percent of the engagement surfacean active conductor of electrical energy. It can be understood that theengaged tissue initially will have a substantially uniform impedance toelectrical current flow, which will increase substantially as theengaged tissue loses moisture due to ohmic heating. Following anarbitrary time interval (in the microsecond to ms range), the impedanceof the engaged tissue—reduced to membrane thickness—will be elevated intemperature and conduct heat to the matrix CM. In turn, the matrix CMwill constantly adjust microcurrent flow therethrough—with each squaremicron of surface area effectively delivering its own selected level ofpower depending on the spatially-local temperature. This automaticreduction of localized microcurrents in tissue thus prevents anydehydration of the engaged tissue. By maintaining the desired level ofmoisture in tissue proximate to the engagement plane(s), the jawassembly can insure the effective denaturation of tissue constituents tothereafter create a strong weld.

By the above-described mechanisms of causing the matrix CM to bemaintained in a selected treatment range, the actual Rf energy appliedto the engaged tissue et can be precisely modulated, practicallypixel-by-pixel, in the terminology used above to describe FIG. 2.Further, the elements 192 in the matrix CM can comprise a substantialvolume of the jaws' bodies and the thermal mass of the jaws, so thatwhen elevated in temperature, the jaws can deliver energy to the engagedtissue by means of passive conductive heating—at the same time Rf energydelivery in modulated as described above. This balance of active Rfheating and passive conductive heating (or radiative, convectiveheating) can maintain the targeted temperature for any selected timeinterval.

Of particular interest, the above-described method of the invention thatallows for immediate modulation of ohmic heating across the entirety ofthe engaged membrane is to be contrasted with prior art instruments thatrely on power modulation based on feedback from a temperature sensor. Insystems that rely on sensors or thermocouples, power is modulated onlyto an electrode in its totality. Further, the prior art temperaturemeasurements obtained with sensors is typically made at only at a singlelocation in a jaw structure, which cannot be optimal for each micron ofthe engagement surface over the length of the jaws. Such temperaturesensors also suffer from a time lag. Still further, such prior arttemperature sensors provide only an indirect reading of actual tissuetemperature—since a typical sensor can only measure the temperature ofthe electrode.

Other alternative modes of operating the conductive-resistive matrixsystem are possible. In one other mode of operation, the systemcontroller 182 coupled to voltage source 180 can acquire data fromcurrent flow circuitry that is coupled to the first and second polarityconductors in the jaws (in any locations described previously) tomeasure the blended impedance of current flow between the first andsecond polarity conductors through the combination of (i) the engagedtissue and (ii) the matrix CM. This method of the invention can providealgorithms within the system controller 182 to modulate, or terminate,power delivery to the working end based on the level of the blendedimpedance as defined above. The method can further include controllingenergy delivery by means of power-on and power-off intervals, with eachsuch interval having a selected duration ranging from about 1microsecond to one second. The working end and system controller 182 canfurther be provided with circuitry and working end components of thetype disclosed in Provisional U.S. Patent Application Ser. No.60/339,501 filed Nov. 9, 2001 titled Electrosurgical Instrument, whichis incorporated herein by reference.

In another mode of operation, the system controller 182 can be providedwith algorithms to derive the temperature of the matrix CM from measuredimpedance levels—which is possible since the matrix is engineered tohave a selected unique resistance at each selected temperature over atemperature-resistance curve (see FIG. 6). Such temperature measurementscan be utilized by the system controller 182 to modulate, or terminate,power delivery to engagement surfaces based on the temperature of thematrix CM. This method also can control energy delivery by means of thepower-on and power-off intervals as described above.

FIGS. 10–11 illustrate a sectional views of an alternative jaw structure100C—in which both the lower and upper engagement surfaces 155A and 155Bcarry a similar conductive-resistive matrices indicated at CM_(A) andCM_(B). It can be easily understood that both opposing engagementsurfaces can function as described in FIGS. 7A–7B and 8A–8B to applyenergy to engaged tissue. The jaw structure of FIGS. 10–11 illustratethat the tissue is engaged on opposing sides by a conductive-resistivematrix, with each matrix CM_(A) and CM_(B) in contact with an opposingpolarity electrode indicated at 165 and 185, respectively. It has beenfound that providing cooperating first and second conductive-resistivematrices in opposing first and second engagement surfaces can enhanceand control both active ohmic heating and the passive conduction ofthermal effects to the engaged tissue.

3. Type “B” conductive-resistive matrix system for tissue welding. FIGS.12 and 14A–14C illustrate an exemplary jaw assembly 200 that carries aType “B” conductive-resistive matrix system for (i) controlling Rfenergy density and microcurrent paths in engaged tissue, and (ii) forcontemporaneously controlling passive conductive heating of the engagedtissue. The system again utilizes an elastomeric conductive-resistivematrix CM although substantially rigid conductive-resistive matrices ofa ceramic positive-temperature coefficient material are also describedand fall within the scope of the invention. The jaw assembly 200 iscarried at the distal end of an introducer member, and can be ascissor-type structure (cf. FIG. 4) or a transecting-type jaw structure(cf. FIGS. 3A–3B). For convenience, the jaw assembly 200 is shown as ascissor-type instrument that allows for clarity of explanation.

The Type “A” system and method as described above in FIGS. 5 and 7A–7Ballowed for effective pixel-by-pixel power modulation—wherein microscalespatial locations can be considered to apply an independent power levelat a localized tissue contact. The Type “B” conductive-resistive matrixsystem described next not only allows for spatially localized powermodulation, it additionally provides for the timing and dynamiclocalization of Rf energy density in engaged tissues—which can thuscreate a “wave” or “wash” of a controlled Rf energy density across theengaged tissue reduced to membrane thickness.

Of particular interest, referring to FIG. 12, the Type “B” systemaccording to the invention provides an engagement surface layer of atleast one jaw 212A and 212B with a conductive-resistive matrix CMintermediate a first polarity electrode 220 having exposed surfaceportion 222 and second polarity electrode 225 having exposed surfaceportion 226. Thus, the microcurrents within tissue during a briefinterval of active heating can flow to and from said exposed surfaceportions 222 and 226 within the same engagement surface 255A. Byproviding opposing polarity electrodes 220 and 225 in an engagementsurface with an intermediate conductive-resistive matrix CM, it has beenfound that the dynamic “wave” of energy density (ohmic heating) can becreated that proves to be a very effective means for creating a uniformtemperature in a selected cross-section of tissue to thus provide veryuniform protein denaturation and uniform cross-linking on thermalrelaxation to create a strong weld. While the opposing polarityelectrodes 220 and 225 and matrix CM can he carried in both engagementsurfaces 255A and 255B, the method of the invention can be more clearlydescribed using the exemplary jaws of FIG. 11 wherein the upper jaw'sengagement surface 250B is an insulator indicated at 252.

More in particular, referring to FIG. 12, the first (lower) jaw 212A isshown in sectional view with a conductive-resistive matrix CM exposed ina central portion of engagement surface 255A. A first polarity electrode220 is located at one side of matrix CM with the second polarityelectrode 225 exposed at the opposite side of the matrix CM. In theembodiment of FIG. 12, the body or support structure 258 of the jawcomprises the electrodes 220 and 225 with the electrodes separated byinsulated body portion 262. Further, the exterior of the jaw body iscovered by an insulator layer 261. The matrix CM is otherwise in contactwith the interior portions 262 and 264 of electrodes 220 and 225,respectively.

The jaw assembly also can carry a plurality of alternating opposingpolarity electrode portions 220 and 225 with intermediateconductive-resistive matrix portions CM in any longitudinal, diagonal ortransverse arrangements as shown in FIGS. 13A–13C. Any of thesearrangements of electrodes and intermediate conductive-resistive matrixwill function as described below at a reduced scale—with respect to anypaired electrodes and intermediate matrix CM.

FIGS. 14A–14C illustrate sequential views of the method of using of theengagement surface layer of FIG. 11 to practice the method of theinvention as relating to the controlled application of energy to tissue.For clarity of explanation, FIGS. 14A–14C depict exposed electrodesurface portions 220 and 225 at laterally spaced apart locations with anintermediate resistive matrix CM that can create a “wave” or “front” ofohmic heating to sweep across the engaged tissue et. In FIG. 14A, theupper jaw 212B and engagement surface 250B is shown in phantom view, andcomprises an insulator 252. The gap dimension g is not to scale, asdescribed previously, and is shown with the engaged tissue having asubstantial thickness for purposes of explanation.

FIG. 14A provides a graphic illustration of the matrix CM withinengagement surface layer 250A at time T₁—the time at which electricalpotential of a first polarity (indicated at +) is applied to electrode220 via an electrical lead from voltage source 180 and controller 182.In FIGS. 14A–14C, the spherical graphical elements 162 of the matrix arenot-to-scale and are intended to represent a “region” of conductiveparticles within the non-conductive elastomer 164. The graphicalelements 162 thus define a polarity at particular microsecond in timejust after the initiation of power application. In FIG. 14A, the bodyportion carrying electrode 225 defines a second electrical potential (−)and is coupled to voltage source 180 by an electrical lead. As can beseen in FIG. 14A, the graphical elements 162 are indicated as having atransient positive (+) or negative (−) polarity in proximity to theelectrical potential at the electrodes. When the graphical elements 162have no indicated polarity (see FIGS. 14B & 14C), it means that thematrix region has been elevated to a temperature at the matrix'switching range wherein electrical conductance is limited, asillustrated in that positively sloped temperature-resistance curve ofFIG. 6 and the graphical representation of FIG. 8B.

As can be seen in FIG. 14A, the initiation of energy application at timeT₁ causes microcurrents me within the central portion of the conductivematrix CM as current attempts to flow between the opposing polarityelectrodes 220 and 225. The current flow within the matrix CM in turnlocalizes corresponding microcurrents mc′ in the adjacent engaged tissueet. Since the matrix CM is engineered to conduct electrical energythereacross between opposing polarities at about the same rate astissue, when both the matrix and tissue are at about 37° C., the matrixand tissue initially resemble each other, in an electrical sense. At theinitiation of energy application at time T₁, the highest Rf energydensity can be defined as an “interface” indicated graphically at planeP in FIG. 14A, which results in highly localized ohmic heating anddenaturation effects along that interface which extends from the matrixCM into the engaged tissue. Thus, FIG. 14A provides a simplifiedgraphical depiction of the interface or plane P that defines the“non-random” localization of ohmic heating and denaturationeffects—which contrasts with all prior art methods that cause entirelyrandom microcurrents in engaged tissue. In other words, the interfacebetween the opposing polarities wherein active Rf heating is preciselylocalized can be controlled and localized by the use of the matrix CM tocreate initial heating at that central tissue location.

Still referring to FIG. 14A, as the tissue is elevated in temperature inthis region, the conductive-resistive matrix CM in that region iselevated in temperature to its switching range to become substantiallynon-conductive (see FIG. 6) in that central region.

FIG. 14B graphically illustrates the interface or plane P at time T₂—anarbitrary microsecond or millisecond time interval later than time T₁.The dynamic interface between the opposing polarities wherein Rf energydensity is highest can best be described as planes P and P′ propagatingacross the conductive-resistive matrix CM and tissue that are defined by“interfaces” between substantially conductive and non-conductiveportions of the matrix—which again is determined by the localizedtemperature of the matrix. Thus, the microcurrent mc′ in the tissue isindicated as extending through the tissue membrane with the highest Rfdensity at the locations of planes P and P′. Stated another way, thesystem creates a front or wave of Rf energy density that propagatesacross the tissue. At the same time that Rf density (ohmic heating) inthe localized tissue is reduced by the adjacent matrix CM becomingnonconductive, the matrix CM will begin to apply substantial thermaleffects to the tissue by means of passive conductive heating asdescribed above.

FIG. 14C illustrates the propagation of planes P and P′ at time T₃—anadditional arbitrary time interval later than T₂. Theconductive-resistive matrix CM is further elevated in temperature behindthe interfaces P and P′ which again causes interior matrix portions tobe substantially less conductive. The Rf energy densities thus propagatefurther outward in the tissue relative to the engagement surface 255A asportions of the matrix change in temperature. Again, the highest Rfenergy density will occur at generally at the locations of the dynamicplanes P and P′. At the same time, the lack of Rf current flow in themore central portion of matrix CM can cause its temperature to relax tothus again make that central portion electrically conductive. Theincreased conductivity of the central matrix portion again is indicatedby (+) and (−) symbols in FIG. 14C. Thus, the propagation of waves of Rfenergy density will repeat itself as depicted in FIGS. 14A–14C which caneffectively weld tissue.

Using the methods described above for controlled Rf energy applicationwith paired electrodes and a conductive-resistive matrix CM, it has beenfound that time intervals ranging between about 500 ms and 4000 ms canbe sufficient to uniformly denature tissue constituents re-crosslink tofrom very strong welds in most tissues subjected to high compression.Other alternative embodiments are possible that multiply the number ofcooperating opposing polarity electrodes 220 and 225 and intermediate orsurrounding matrix portions CM.

FIG. 15 depicts an enlarged view of the alternative Type “B” jaw 212A ofFIG. 13A wherein the engagement surface 250A carries a plurality ofexposed conductive matrix portions CM that are intermediate a pluralityof opposing polarity electrode portions 220 and 225. This lower jaw 212Ahas a structural body that comprises the electrodes 220 and 225 and aninsulator member 266 that provide the strength required by the jaw. Aninsulator layer 261 again is provided on outer surfaces of the jawexcepting the engagement surface 255A. The upper jaw (not shown) of thejaw assembly can comprise an insulator, a conductive-resistive matrix,an active electrode portion or a combination thereof. In operation, itcan be easily understood that each region of engaged tissue between eachexposed electrode portion 222 and 226 will function as described inFIGS. 14A–14C.

The type of engagement surface 250A shown in FIG. 15 can have electrodeportions that define an interior exposed electrode width ew rangingbetween about 0.005″ and 0.20″ with the exposed outboard electrodesurface 222 and 226 having any suitable dimension. Similarly, theengagement surface 250A has resistive matrix portions that portions thatdefine an exposed matrix width mw ranging between about 0.005″ and0.20″.

In the embodiment of FIG. 15, the electrode portions 220 and 225 aresubstantially rigid and extend into contact with the insulator member266 of the jaw body thus substantially preventing flexing of theengagement surface even though the matrix CM may be a flexible siliconeelastomer. FIG. 16 shows an alternative embodiment wherein the electrodeportions 220 and 225 are floating within, or on, the surface layers ofthe matrix 250A.

FIG. 17 illustrates an alternative Type “B” embodiment that is adaptedfor further increasing passive heating of engaged tissue when portionsof the matrix CM are elevated above its selected switching range. Thejaws 212A and 212B and engagement surface layers 255A and 255B bothexpose a substantial portion of matrix to the engaged tissue. Theelastomeric character of the matrix can range between about 20 and 95 inthe Shore A scale or above about 40 in the Shore D scale. Preferably,one or both engagement surface layers 255A and 255B can be “crowned” orconvex to insure that the elastomeric matrices CM tend to compress theengaged tissue. The embodiment of FIG. 17 illustrates that a firstpolarity electrode 220 is a thin layer of metallic material that floatson the matrix CM and is bonded thereto by adhesives or any othersuitable means. The thickness of floating electrode 220 can range fromabout 1 micron to 200 microns. The second polarity electrode 225 hasexposed portions 272 a and 272 b at outboard portions of the engagementplanes 255A and 255B. In operation, the jaw structure of FIG. 17 createscontrolled thermal effects in engaged tissue by several different means.First, as indicated in FIGS. 18A–18C, the dynamic waves of Rf energydensity are created between the opposing polarity electrode portions 220and 225 and across the intermediate matrix CM exactly as describedpreviously. Second, the electrically active components of the upperjaw's engagement surface layer 255B cause microcurrents between theengagement surface layers 255A and 255B, as well as to the outboardexposed electrode surfaces exposed portions 272 a and 272 b, between anyportions of the matrices that are below the selected switching range.Third, the substantial volume of matrix CM is each jaw providessubstantial heat capacity to very rapidly cause passive heating oftissue after active tissue heating is reduced by increasing impedance inthe engaged tissue et.

FIG. 19 illustrates another Type “B” embodiment of jaws structure thatagain is adapted for enhanced passive heating of engaged tissue whenportions of the matrix CM are elevated above its selected switchingrange. The jaws 212A and 212B and engagement surface layers 255A and255B again expose matrix portions to engaged tissue. The upper jaw'sengagement surface layer 255B is convex and has an elastomeric hardnessranging between about 20 and 80 in the Shore A scale and is fabricatedas described previously.

Of particular interest, the embodiment of FIG. 19 depicts a firstpolarity electrode 220 that is carried in a central portion ofengagement plane 255A but the electrode does not float as in theembodiment of FIG. 17. The electrode 220 is carried in a first matrixportion CM₁ that is a substantially rigid silicone or can be a ceramicpositive temperature coefficient material. Further, the first matrixportion CM₁ preferably has a differently sloped temperature-resistanceprofile (cf. FIG. 6) that the second matrix portion CM₂ that is locatedcentrally in the jaw 212A. The first matrix portion CM₁, whethersilicone or ceramic, has a hardness above about 90 in the Shore A scale,whereas the second matrix portion CM₂ is typically of a silicone asdescribed previously with a hardness between about 20 and 80 in theShore A scale. Further, the first matrix portion CM₁ has a higherswitching range than the second matrix portion CM₂. In operation, thewave of Rf density across the engaged tissue from electrode 220 tooutboard exposed electrode portions 272 a and 272 b will be induced bymatrix CM₁ having a first higher temperature switching range, forexample between about 70° C. to 80° C., as depicted in FIGS. 18A–18C.The rigidity of the first matrix CM₁ prevents flexing of the engagementplane 255A. During use, passive heating will be conducted in an enhancedmanner to tissue from electrode 220 and the underlying second matrix CM₂which has a second selected lower temperature switching range, forexample between about 60° C. to 70° C. This Type “B” system has beenfound to be very effective for rapidly welding tissue—in part because ofthe increased surface area of the electrode 220 when used in smallcross-section jaw assemblies (e.g., 5 mm. working ends).

FIG. 20 shows the engagement plane 255A of FIG. 17 carried in atransecting-type jaws assembly 200D that is similar to that of FIGS.3A–3B. As described previously, the Type “B” conductive-resistive matrixassemblies of FIGS. 12–19 are shown in a simplified form. Any of theelectrode-matrix arrangements of FIGS. 12–19 can be used in thecooperating sides of a jaw with a transecting blade member-similar tothe embodiment shown in FIG. 20.

3. Type “C” system for tissue welding. FIGS. 21 and 22 illustrate anscissor-type instrument 380 corresponding to the invention having anexemplary Type “C” jaw assembly 400 that carries a conductive-resistivematrix CM that comprises a variably resistive body as describedpreviously for (i) controlling Rf energy density and microcurrent pathsin engaged tissue, and (ii) for contemporaneously controlling passiveconductive heating of the engaged tissue. The variably resistive body ormatrix extends inwardly from the tissue-engaging surface as describedabove. The scissor-type instrument is useful in that it provides veryrapid tissue welding capabilities in an instrument form that is commonlyused in open surgeries. In one preferred embodiment, the scissor-typeinstrument 380 can be fitted with a blade for transecting welded tissue.Of particular interest, the scissor body of the instrument can bereusable with (i) a disposable electrosurgical cartridge 405 and (ii) adisposable blade cartridge 408 (FIG. 23). The blade cartridge 408provides and thin flexible cutting blade that can be moved between afirst retracted position and a second extended position.

In FIGS. 21 and 22, it can be seen that first and second scissor armmembers 410A and 410B carry opposing first and second jaws 412A and 412Bthat define respective tissue-engaging surfaces 455A and 455B. In thisembodiment, the upper jaw 412A and engagement surface 455A are similarto that described in the embodiments of FIG. 20 with aconducive-resistive matrix CM coupled to a voltage source 180 asdescribed previously. The lower jaw's engagement surface 455B can carrya variably resistive matrix as in FIG. 20, a return electrode as inFIGS. 5 and 7A, or can be fully insulated as described in the embodimentof FIGS. 14A–14C. The scissor jaw arms 410A and 410B rotate about pivot460 (FIG. 21).

The scissor-type instrument 380 of FIG. 21 provides jaw working endsthat are in a curved configuration but the jaw portions also can belinear. Such an instrument can apply substantial leverage on theengagement surfaces to thereby apply very high compressive forces on theengaged tissue and thus function optimally to create an effective weldas described above. The handle portion of the scissor jaw arms 410A and410B provides a ratchet-type lock-release mechanism 462 for clamping thejaws closed as is common in the art.

Of particular interest, referring to FIGS. 22 and 23, the re-usableinstrument has a replaceable, disposable cartridge 405 that carries aconductive-resistive matrix CM. FIG. 23 shows the cartridge 405 de-matedfrom the scissor arm 410A and indicates how the cartridge fits into arecessed receiving portion 464 of upper jaw 412A. At least one pin orprojecting element 466 cooperates with openings 468 in the jaw portion(see FIG. 22) to insure that the cartridge is positioned properly andlocked in place. In the embodiment shown in FIGS. 21–23, the cartridge405 has an axial channel or slot 470 a therein that cooperates with anoptional slidable blade element 475. As can be seen in FIG. 22, when thejaws carry opposing polarity exposed electrodes or conductive matricesCM, at least one jaw carries an insulated projecting element 476 alongan edge of the jaw (or along an edge of the central blade channel) toprevent the opposing polarity components from contacting one anotherwhen the jaws are in the closed position.

The cartridge 405 has an electrical lead 478 with and insulative coating480 that extends proximally to connector 482 that clips on to acooperating member 484 of the scissor arm (FIG. 23). An electrical cable485 extending from the voltage source 180 couples to the connector 482to provide Rf energy to the instrument.

In the type of instrument shown in FIG. 21, the upper jaw portion 412Acarries the conductive-resistive matrix cartridge 405 that cooperatesthe engagement surface 455B of the lower jaw portion 412B. In apreferred embodiment as shown in FIG. 22, the lower jaw portion 412Bcarries a cooperating variably resistive matrix CM of the type shown inFIGS. 19 and 20. As can be seen in FIG. 22, the conductive-resistivematrix CM in the lower jaw's engagement surface 455B has an axialchannel or slot 470 b therein that receives the slidable blade element475. The conductive-resistive matrix CM of the lower scissor jaw can beadapted to be a permanent component that is sterilizable and that doesnot require replacement after each use. Alternatively, theconductive-resistive matrix CM of the lower scissor jaw can be made tobe a disposable cartridge. In the embodiments that require electricalfunctionality in each jaw, the leads or leads from the voltage source180 can be carried from the first scissor arm 410A to the second scissorarm 410B across the pivot pin 460 as is known the art so that the cable485 from the voltage source 180 needs to be coupled to only one scissorarm.

FIG. 23 also shows the instrument 380 with a de-mated disposable bladecartridge 408 that can be snap-fit into the second scissor arm 410B. Thedisposable blade cartridge 408 has a flexible blade element 475 coupledto a medial shaft portion 486 that carries a plastic grip member 488 atis proximal end. The blade cartridge 408 is fabricated so that themedial shaft portion 486 is releasably and slidably locked into acooperated slot 490 in a member 492 carried by the second scissor arm410B.

The instrument 380 of FIGS. 21 and 23 further includes a safety featuresthat comprise first and second interlocks as are known in the art. Thefirst interlock built into the blade cartridge 408 and the scissor arms410A and 410B allows the blade 475 to slide distally to its secondextended position in the jaw portions only when the scissor arms andjaws are rotated to the second closed position. The second safetyinterlock mechanism built into blade cartridge 408 and the scissor armsprevents the rotation of the scissor arms to the first open position atany time the blade 475 to is still in its second extended position. Onlyafter the blade 475 is moved back to its first retracted position canthe scissor arms be opened.

In another embodiment shown in FIG. 24, it should be appreciated thatthe cutting blade element need not be a reciprocating blade 475 as shownin FIGS. 21–23. Rather, FIG. 24 illustrates that a scissor-type bladeelement 495 that rotates with the scissor arm 410A can be provided. Itcan easily be understood that the blade element 495 can be adapted toautomatically rotate fully into the blade slots 470 a and 470 b to cutthe tissue after the engagement surfaces 455A and 455B clamp against thetissue. Alternatively, an interlock can be provided to only rotate theblade to cut the tissue after the tissue is welded and the physicianelects to transect the tissue by rotating the blade to cut the tissue.

In another embodiment corresponding to the invention, theelectrosurgical working end carries an exposed electrical lead portionthat extends to the electrode or conductive-resistive matrix CM. Forexample, the instrument 380 of FIG. 21 has exposed electrical lead 480.It should be appreciated that the scope of the invention extends to anymedical device working end. It has been found that visual signals may bethe optimal means of informing a physician intraoperatively of thestatus of energy delivery to tissue, whether in an endoscopic or opensurgery. For example, audio tones are often used to alert the physicianas to on/off energy delivery modes.

In another embodiment (not shown) a scissor-type instrument similar tothat of FIG. 21 can have a first jaw portion that is adapted to receivean electrosurgical cartridge and a second jaw that has permanent blade.The blade can have a first recessed position wherein the jaws'engagement surfaces can be locked to together and a second exposedposition wherein the scissor arm are closed further to cause the bladeto cross the plane between the engagement surfaces to cut the tissue.

Referring to FIG. 25, the present invention provides an electrical lead504 with series of layers that collectively provide an insulativecoating that changes from a first color to a second “signal” color whenelectrical current is flowing through the lead 504. Alternatively, thelead can change between a range of colors that can indicate to asignificant extent the impedance of the engaged tissue. The electricallead can be an exposed wire lead 478 as shown in FIGS. 23 and 25 or itcan be a thin film conductor element 508 laminated on a surface of theinstrument as depicted in FIG. 26.

In one exemplary inexpensive printed and laminated embodiment, as shownin FIG. 26, the invention comprises a conductor element 508 with a thinconductive-resistive matrix 510 (or a conductive ink) printed over theconductor 508. A thermochromic ink layer 512 is then printed over theconductor 508 and matrix 510. A thermochromic ink can be engineered toundergo a thermochromic transition and change its color after it reachesa selected temperature. A final insulative transparent layer 514 isapplied over the thermochromic layer 512, or more preferably thethermochromic composition is integrated into the insulator layer. Byapplying such layers over a substrate, it is possible to create anextremely inexpensive printed component (e.g., a flex circuit component)that changes in temperature depending on the amount of electricitytransmitted through the lead which heats the matrix and then causes areversible thermochromic transition in layer 512 at a selectedtemperature. The conductor element 508 can be coverer by either apositive or negative temperature coefficient matrix 510 that defines aselected switching range to cause current to reach the thermochromiclayer, with an optional second layer of an opposing polarity conductorto thus engineer the thermochromic layer 512 to change color at anyselected event that would provide useful information to the physician,such as a change in temperature, a change in current flow, a changeimpedance in the engaged tissue, or a short circuit in the system.

FIG. 25 shows similar layers of cable-type conductor element 508,conductive-resistive matrix 510 and thermochromic layer 512 in the formof a round wire lead that can function as described above. Co-pendingU.S. patent application Ser. No. 10/441,519 filed May 20, 2003 titled“Electrosurgical Working End with Thermochromic or PiezochromicIndicators”, incorporated herein by reference, provides furtherdisclosures of thermochromic compositions in a coating about the surfaceof a working end to indicate temperature.

There are two types of thermochromic ink: liquid crystal and leucodyetypes. A liquid crystal based thermochromic ink is sensitive to verysmall changes in temperature. Leucodyes are specially formulatedsubstances that change from a specific color to a clear state whensubjected to a temperature change of about 5 degrees F. or more.Thermochromic inks can be formulated to change color at specifictemperatures, which can be selected along with the matrix resistancecharacterstics as described above. The thermochromic portion of the leadis typically in the working end, but also can be in the handle or medialintroducer portion of the instrument.

Although particular embodiments of the present invention have beendescribed above in detail, it will be understood that this descriptionis merely for purposes of illustration. Specific features of theinvention are shown in some drawings and not in others, and this is forconvenience only and any feature may be combined with another inaccordance with the invention. Further variations will be apparent toone skilled in the art in light of this disclosure and are intended tofall within the scope of the appended claims.

1. A bipolar electrosurgical instrument, the instrument comprising: aworking end having first and second openable-closeable jaws having firstand second respective tissue-engaging surfaces for engaging tissue andfirst and second respective support structures; the firsttissue-engaging surface comprising a portion of the first supportstructure and a polymeric body, the first support structure configuredas a first polarity electrode and at least partially surrounding thepolymeric body. the polymeric body having a transverse cross sectioncomprising a significant fractional area of a transverse cross sectionof the first jaw, the polymeric body having a non-linear positivelysloped temperature resistance profile in a selected tissue treatmentrange; and the second tissue-engaging surface comprising a secondpolarity electrode.
 2. The bipolar electrosurgical instrument of claim1, wherein the second tissue-engaging surface further comprises aportion of the second support structure.
 3. The bipolar electrosurgicalinstrument of claim 2, wherein the second tissue-engaging surfacefurther comprises another polymeric body, the other polymeric bodyextending inwardly from the second tissue-engaging surface and having atransverse cross section comprising a significant fractional area of atransverse cross section of the second jaw, the other polymeric bodyhaving a non-linear positively sloped temperature resistance profile ina selected tissue treatment range.
 4. The bipolar electrosurgicalinstrument of claim 3, wherein the second support structure at leastpartially surrounds the other polymeric body.
 5. The bipolarelectrosurgical instrument of claim 3, wherein the second supportstructure is configured as a first polarity electrode.
 6. A bipolarelectrosurgicul instrument, the instrument comprising: a working endhaving first and second openable-closeable jaws comprising first andsecond respective tissue-engaging surfaces for engaging tissue and firstand second respective support structures, the first tissue-engagingsurface comprising a first polarity electrode, the secondtissue-engaging surface comprising a second polarity electrode; and apolymeric body extending inwardly from the second tissue-engagingsurface and partially surrounded by the second support structure, thepolymeric body having a transverse cross section comprising asignificant fractional area of a transverse cross section of the secondjaw, the second jaw transverse cross section comprising a supportstructure cross section and the polymeric body cross section, thepolymeric body having a non-linear positively sloped temperatureresistance profile defining a temperature treatment range for weldingtissue.
 7. The bipolar electrosurgical instrument of claim 6, whereinthe first tissue-engaging surface further comprises a second polarityelectrode.
 8. The bipolar electrosurgical instrument of claim 6, furthercomprising: another polymeric body extending inwardly from the firsttissue-engaging surface, the another polymeric body having a transversecross section comprising a significant fractional area of a transversecross section of the first jaw, the first jaw transverse cross sectioncomprising a support structure cross section and the another polymericbody cross section, the other polymeric body having a non-linearpositively sloped temperature resistance profile defining a temperaturetreatment range for welding tissue.